Process for recovering cobalt carbonyl catalysts used to produced N-acyl-alpha-amino acid derivatives by amidocarbonylation

ABSTRACT

The present invention relates to a process for recovering cobalt carbonyl catalysts used in the preparation of N-acyl-alpha-amino acid derivatives by amidocarbonylation comprising the process steps: 
     adding aqueous hydrogen peroxide solution to the reaction solution present after the preparation of the N-acyl-α-amino acid derivative, 
     then separating the aqueous phase containing water-soluble cobalt(II) salt from the nonaqueous product-containing phase, 
     subsequently adding an alkali metal salt of the N-acyl-alpha-amino acid derivative to the aqueous phase from the previous process step, 
     then separating off the precipitated cobalt salt of the N-acyl-alpha-amino acid derivative, and 
     finally converting the resulting cobalt salt of the N-acyl-alpha-amino acid derivative into the cobalt carbonyl catalyst in the presence of a mixture of carbon monoxide and hydrogen.

BACKGROUND OF THE INVENTION

Amidocarbonylation is, for the purposes of the present invention, thecarbonylation of carboxamides in the presence of aldehydes and carbonmonoxide or synthesis gas to give N-acyl-alpha-amino acid derivatives.This reaction is carried out in the presence of cobalt carbonylcompounds as homogeneous catalysts. The use of fatty acid amides asamide components and formaldehyde as aldehyde components makes itpossible to employ this process to access the class of N-acylsarcosineswhich are used industrially as surfactants, soaps and emulsifiers.

DESCRIPTION OF THE RELATED ART

A significant part of such a preparative process is the development of acatalyst circuit, i.e. a process for separating the catalyst used whichis dissolved in the reaction medium from the product prepared, itsreprocessing and return to the preparative process.

For cost reasons and to avoid environmental pollution by cobaltcompounds, a recovery process which is as complete as possible and atthe same time simple and inexpensive is required for the cobalt carbonylcatalyst used.

Processes for recovering cobalt catalysts have already been describedfor various reactions.

The Japanese first publications 54-112816 and 58-198441 discloseprocesses for preparing dialkyl malonates by esterification ofalkylmono-haloacetic acid with a lower aliphatic alcohol and carbonmonoxide in the presence of a cobalt carbonyl catalyst and a basiccompound. Subsequent to this esterification, the catalyst is decomposedinto a divalent water-soluble cobalt salt by addition of an aqueoussolution of an inorganic acid, e.g. sulfuric acid, or by addition ofsulfuric acid and oxygen. The aqueous phase thus obtained is separatedfrom the organic phase and the water-soluble cobalt salt is precipitatedfrom it as water-insoluble cobalt hydroxide by addition of alkali metalhydroxide, e.g. sodium hydroxide. After washing, the cobalt hydroxide isfinally converted into the corresponding cobalt carbonyl compound bytreatment with carbon monoxide or carbon monoxide/hydrogen in thepresence of an organic solvent, e.g. an aromatic hydrocarbon or analcohol suitable for the esterification. The cobalt carbonyl catalystobtained in this way is reused for the esterification.

The Japanese first publication 57-183749 describes a process forpreparing α-amino-β-hydroxybutanoic acid in which, in a carbonylationstep which takes place first, epichlorohydrin, carbon monoxide, a basiccompound and an alcohol are reacted to give α-amino-β-hydroxybutanoicacid. In the next process step, the cobalt carbonyl catalyst isdecomposed by addition of mineral acid, e.g. sulfuric acid, and oxygento the reaction solution obtained in the previous process step to form adivalent water-soluble cobalt salt. The alcohol present in the reactionsolution is then removed and water is subsequently added to form atwo-phase system which is separated into an aqueous phase containing thewater-soluble cobalt salt and an organic phase containingα-amino-β-hydroxybutanoic acid. The recovery of the cobalt carbonylcatalyst is carried out by addition of alkali metal hydroxide to theaqueous phase. The cobalt hydroxide precipitate formed is filtered off,washed and subsequently dewatered. Subsequent reaction of the cobalthydroxide with carbon monoxide and hydrogen gives the cobalt carbonylcatalyst back again.

EP-A-0 343 042 relates to a process for preparing dialkyl malonates bycarbonylation of alkyl chloroacetates in the presence of a cobaltcarbonyl catalyst. The recovery of the cobalt carbonyl catalyst used iscarried out in a plurality of process steps, with a water-soluble cobaltsalt first being produced by addition of acid. In the next process step,this cobalt salt is converted into the salt of a fatty acid, e.g. oleicacid, palmitic acid or stearic acid. The desired cobalt carbonylcatalyst is obtained from this fatty acid salt by reaction with carbonmonoxide and hydrogen.

A process for recovering cobalt carbonyl catalysts used in thepreparation of N-acyl-alpha-amino acid derivatives by amidocarbonylationis described in the German Patent Application No. 195 45 641.9 which isprior art according to §3 II of the German Patent Law. In this process,the catalyst present in the reaction solution is converted into awater-soluble cobalt(II) salt by addition of H₂ O₂ and possibly an acid,e.g. sulfuric acid. After phase separation and decomposition of excessH₂ O₂, the aqueous phase containing the cobalt salt is brought to a pHof 12 by means of an alkali metal hydroxide in order to precipitate thecobalt as a cobalt hydroxide precipitate. The cobalt precipitateobtained in this way has to be carefully washed and dried in order toremove entrained salt residues. The pure cobalt hydroxide issubsequently processed with N-acyl-alpha-amino acid derivative to form amelt from which the cobalt carbonyl catalyst is obtained by reactionwith carbon monoxide and hydrogen at elevated temperature and pressure.

However, this process has the disadvantage that it is necessary to workat high pH values, which requires the use of particularly suitableapparatuses. In addition, a considerable amount of sulfate salt (up to10% by weight) is entrained in the precipitation of cobalt as hydroxideand this has to be removed in elaborate washing processes. A furtherdisadvantage is that the reaction of cobalt hydroxide with theN-acyl-alpha-amino acid derivative to form a melt can result in theformation of cobalt hydroxide lumps which react further only slowly.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process forrecovering cobalt carbonyl catalysts used in the preparation ofN-acyl-alpha-amino acid derivatives, in particular N-acylsarcosines, byamidocarbonylation, which process enables the abovementioneddisadvantages to be overcome.

In principle, the following technical difficulties have to be taken intoaccount in such a process in the case of N-acyl-alpha-amino acidderivatives.

The reaction products of the amidocarbonylation, in particular theabovementioned N-acylsarcosines, are not volatile and can therefore notbe removed from the reaction solution by distillation. Distillativerecovery of the cobalt carbonyl catalysts which are volatile in pureform is likewise not possible since they are destroyed on heating thereaction solution, i.e. in the presence of N-acyl-α-amino acidderivatives. Likewise, it has to be noted that the cobalt carbonylcatalysts used for the amidocarbonylation are only partly present asactive cobalt carbonyl catalysts after the reaction and the method ofrecovery therefore has to take into account a number of different cobaltcarbonyl compounds.

Moreover, the separation of the cobalt catalysts from the reactionsolution by phase separation into an aqueous, cobalt-containing phaseand an organic, product-containing phase is made more difficult by theformation of complexes of the cobalt compounds and theN-acyl-alpha-amino acid derivatives obtained.

In addition, the cobalt carbonyl catalysts cannot, unlike the case ofhydroformylation, be prepared from Co(II) salts, e.g. cobalt acetate,cobalt oxide and cobalt hydroxide, owing to the mild reaction conditionsduring the carbonylation stage of the amidocarbonylation, but have to beprepared in a prior process step in order to be able to be used in thesubsequent carbonylation stage.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, the above object is achieved by aprocess which comprises the following steps:

adding aqueous hydrogen peroxide solution or adding aqueous hydrogenperoxide solution and a mineral acid to the reaction solution presentafter the preparation of the N-acyl-α-amino acid derivative,

then separating the aqueous phase containing water-soluble cobalt(II)salt from the nonaqueous product-containing phase,

subsequently adding an alkali metal salt of the N-acyl-alpha-amino acidderivative to the aqueous phase from the previous process step,

then separating off the precipitated cobalt salt of theN-acyl-alpha-amino acid derivative, and

finally converting the resulting cobalt salt of the N-acyl-alpha-aminoacid derivative into the cobalt carbonyl catalyst in the presence of amixture of carbon monoxide and hydrogen.

The conversion of the cobalt salt of the N-acyl-alpha-amino acidderivative into the cobalt carbonyl catalyst is usually carried out at atemperature of from 50 to 250° C. and a pressure of from 20 to 250 bar.

The process of the invention enables, in particular, the cobalt carbonylcatalysts used in amidocarbonylation, in particular Co₂ (CO)₈ andHCo(CO)₄, to be recovered. The starting point for this process is thereaction solution present after the preparation of the N-acyl-α-aminoacid derivative, in particular N-acylsarcosine. The process of theinvention is particularly suitable for reaction solutions which areobtained in accordance with the process for preparing N-acyl-α-aminoacid derivatives described in the European Patent Application No. 95 106329.6 (EP-A-0 680 948).

In the first process step, aqueous hydrogen peroxide solution is addedto this reaction solution, whereby firstly the cobaltcarbonyl-N-acyl-alpha-amino acid derivative complexes formed aredestroyed and secondly the cobalt present in the cobalt carbonylcompounds is oxidized to cobalt(II) which forms water-soluble salts.

It has been found that the amount of hydrogen peroxide solution to beadded is advantageously from 0.1 to 5 equivalents, in particular from0.2 to 4 equivalents and particularly preferably from 0.5 to 2equivalents (H₂ O₂, based on cobalt present in the reaction solution).

If the amidocarbonylation has been carried out in a solution containingmineral acid, e.g. sulfuric acid, the addition of further mineral acid,preferably dilute sulfuric acid, to form water-soluble cobalt salts isgenerally not necessary.

Suitable mineral acids are, for example, sulfuric acid, phosphoric acid,hydrochloric acid, phosphorous acid and perchloric acid, with particularpreference being given to sulfuric acid, in particular dilute sulfuricacid.

The aqueous phase containing water-soluble Co(II) salt, e.g. cobalt(II)sulfate, obtained in the first process step is separated from thenonaqueous phase in which the product is present.

If necessary, the cobalt content of the nonaqueous phase can be furtherreduced by repeated addition of water or aqueous acid to the nonaqueousphase containing the N-acyl-α-amino acid derivative, if desired inappropriate extraction apparatuses, e.g. mixer-settler boxes,centrifugal extractor or countercurrent extraction column.

It has been found that excess hydrogen peroxide which is present in theaqueous phase after the phase separation can lead, under theprecipitation conditions preferred according to the invention, viz.approximately pH>7 to the formation of water-containing cobalt(III)hydroxide which is stable in alkaline medium and is formed as a veryfine precipitate which is difficult to filter.

In a preferred embodiment of the process of the invention, the excesshydrogen peroxide is therefore removed before precipitation of thecobalt as cobalt salt of the N-acyl-alpha-amino acid derivative. It isusually removed by heating the aqueous phase, preferably to the boilingpoint.

If desired, the aqueous phase can be neutralized with alkali metalhydroxide, preferably sodium and/or potassium hydroxide, before heating.

It is industrially advantageous to heat the aqueous phase under reducedpressure and at the same time distil off any solvent still dissolved inthe aqueous phase.

According to the invention, cobalt is then obtained from the aqueousphase, from which the excess hydrogen peroxide has been removed ifdesired, as a water-insoluble precipitate of the cobalt salt of theN-acyl-alpha-amino acid derivative by addition of an alkali metal saltof the corresponding N-acyl-alpha-amino acid derivative, preferably analkali metal N-acylsarcosinate, particularly preferably sodium and/orpotassium N-lauroylsarcosinate.

The alkali metal salt of the N-acyl-amino acid derivative is preferablyadded in the form of a 30% strength by weight aqueous solution. Afteraddition of the alkali metal salt of the N-acyl-amino acid derivative,the pH of the aqueous phase is preferably about 7.

In order to achieve as complete a precipitation as possible, it isadvantageous if the concentration of the water-soluble cobalt salt inthe aqueous phase does not exceed 2% by weight.

The resulting water-insoluble precipitate of the cobalt salt of theN-acyl-alpha-amino acid derivative is separated from the aqueous phaseby customary means, for example filtration.

The precipitate obtained by the process of the invention generallycontains less than 0.2% by weight of salt of the acid used, in the caseof sulfuric acid sulfate salt. If necessary, any salt residue stillpresent can be removed by washing the precipitate with water without asignificant loss of cobalt ions with the washing water occurring.However, it has been found to be advantageous in the process of theinvention for the precipitate of cobalt salt of the N-acyl-alpha-aminoacid derivative to be very substantially free of other salts.

The precipitate can be dried before further processing. In general, theair-dried precipitate still contains 3 mol of water per mol of cobalt.

The above-described air-dried precipitate of cobalt salt of theN-acyl-alpha-amino acid derivative can, if desired, be dried further atfrom 50 to 100° C. and from 10 to 100 torr and the water content canthus be reduced to 1 mol of water per mol of cobalt. However, thisdrying is generally not necessary for the process of the invention.

The conversion of the resulting cobalt salt of the N-acyl-alpha-aminoacid derivative into the cobalt carbonyl catalyst is preferably carriedout in a polar, aprotic solvent which can also be used in the subsequentamidocarbonylation as solvent for the cobalt carbonyl catalyst recoveredby means of the process of the invention. Particularly suitable solventshave been found to be tetrahydrofuran, glycol dimethyl ether, tert-butylmethyl ether, diglycol dimethyl ether, dimethylformamide,dimethylacetamide, butyl acetate, acetonitrile and N-acylsarcosines.Particular preference is given to using tetrahydrofuran, tert-butylmethyl ether, N-acylsarcosines and glycol dimethyl ether.

For the conversion, the cobalt salt of the N-acyl-alpha-amino acidderivative is reacted with carbon monoxide or a mixture of carbonmonoxide and hydrogen, known as synthesis gas, at a temperature of from50 to 250° C. and a pressure of from 40 to 250 bar, preferably from 60to 200 bar, particularly preferably from 80 to 180 bar. The compositionof the carbon monoxide/hydrogen mixture is preferably from 4:1 to 1:4.The cobalt carbonyl catalyst thus obtained can be used withoutlimitation for the amidocarbonylation.

According to a particular embodiment, the dried or undried cobalt saltof the N-acyl-alpha-amino acid derivative is mixed with furtherN-acyl-alpha-amino acid derivative before conversion into the cobaltcatalyst and processed by heating and stirring to form a melt which issubsequently used as starting material for the conversion into thecobalt catalyst.

Here, the molar ratio of cobalt salt of the N-acyl-alpha-amino acidderivative to N-acyl-alpha-amino acid derivative is usually 1:2-5,preferably 1:2.5-4.

A further advantage of the process of the invention is that any cobaltresidues still present in the aqueous phase after the precipitation canbe recovered and processed so that complete recycling is ensured.

The remaining aqueous phase usually still contains from 10 to 1000 ppmof cobalt. This remaining cobalt can be separated off, for example, byfiltration through an ion exchanger. The ion exchanger can here be usedto exhaustion. The cobalt-laden ion exchanger can be regenerated by, forexample, washing with sodium sulfate solution so that the ion exchangeris again ready for further cobalt recovery. The solution containingcobalt sulfate and sodium sulfate obtained by washing can be added tothe reaction solution used for the first stage of the process of theinvention without the process of the invention being adversely affected.

The following examples illustrate the process of the invention.

PREPARATIVE EXAMPLES

The following examples concern the recovery of cobalt carbonyl catalystused in the preparation of lauroylsarcosine by amidocarbonylation. Thestarting solution used was the following reaction solution obtained inthe amidocarbonylation.

110 l of reaction solution having a density of 0.818 kg/l had thefollowing composition: 60% of N-lauroylsarcosine (product), 39% ofsolvent (tertbutyl methyl ether), 0.44% of sulfuric acid, 0.13% ofcobalt, 0.35% of formaldehyde and about 0.04% of methylamine. 300 ml of32% strength hydrogen peroxide solution in water were added and themixture was stirred for 30 minutes at 50° C. After addition of 15 l ofwater, the phases were separated and 12 l of aqueous phase and 113 l ofproduct phase were obtained. The aqueous phase contained about 1% oftert-butyl methyl ether, 0.98% of cobalt, 2% of formaldehyde, 1% ofmethyl-ammonium sulfate, about 2.5% of sulfuric acid and an undeterminedamount of hydrogen peroxide.

The following examples were each carried out using 1 l of this aqueoussolution.

Example 1

1000 ml of the cobalt solution resulting from separation of the organicphase and containing sulfuric acid, residues of hydrogen peroxide and0.98% by weight of Co are adjusted to a pH of 6.5 by addition of about130 g of 18% strength by weight sodium hydroxide solution andsubsequently freed of hydrogen peroxide by heating to the boiling point.333 ml of aqueous 1M sodium N-lauroylsarcosinate are subsequently added,forming cobalt N-lauroylsarcosinate in the form of a pale pinkprecipitate.

The precipitate is filtered off and washed with about 200 ml of water inorder to remove any sulfate residues still present.

The cobalt N-lauroylsarcosinate obtained (260 g) is slurried in 260 g ofN-lauroylsarcosine (about 3 molar equivalents) and the viscoussuspension is heated to 120° C. while stirring. The cobalt-containingmelt is freed of the water present under reduced pressure (pressure: 50mbar). The residue is subsequently dissolved in 500 ml of methyl-t-butylether (MTBE) and carbonylated with synthesis gas (CO:H₂ ratio=2:1) at120 bar in a steel autoclave. The reaction is carried out at from 70 to90° C.

The cobalt carbonyl formed can be used without limitation for theamidocarbonylation.

Example 2

1000 ml of a cobalt solution resulting from separation of the organicphase and containing sulfuric acid, residues of hydrogen peroxide and0.98% by weight of Co are adjusted to a pH of 6.5 by addition of about130 g of 18% strength by weight sodium hydroxide solution andsubsequently freed of hydrogen peroxide by heating to the boiling point.

333 ml of aqueous 1M sodium N-lauroylsarcosinate are subsequently added,forming cobalt N-lauroylsarcosinate in the form of a pale pinkprecipitate.

The precipitate is filtered off and washed with about 200 ml of water inorder to remove any sulfate residues still present.

The cobalt N-lauroylsarcosinate (260 g) is dried at room temperature(then 220 g), slurried in 500 ml of MTBE (about 2 molar equivalents) andthe suspension is carbonylated with synthesis gas (CO:H₂ ratio=2:1) at120 bar in a steel autoclave. The reaction is carried out at from 70 to90° C. The cobalt carbonyl formed can be used without limitation for theamidocarbonylation.

Example 3

1000 ml of a cobalt solution resulting from separation of the organicphase and containing sulfuric acid, residues of hydrogen peroxide and0.98% by weight of Co are adjusted to a pH of 6.5 by addition of about130 g of 18% strength by weight sodium hydroxide solution andsubsequently freed of hydrogen peroxide by heating to the boiling point.

333 ml of aqueous 1M sodium N-lauroylsarcosinate are subsequently added,forming cobalt N-lauroylsarcosinate in the form of a pale pinkprecipitate.

The precipitate is filtered off and washed with about 200 ml of water inorder to remove any sulfate residues still present.

The cobalt N-lauroylsarcosinate dried to constant weight at 75-80° C.and 30 torr (205 g) is dissolved in 500 ml of MTBE and carbonylated withsynthesis gas (CO:H₂ ratio=2:1) at 120 bar in a steel autoclave. Thereaction is carried out at from 70 to 90° C.

The cobalt carbonyl formed can be used without limitation for theamidocarbonylation.

Example 4

The procedure of Example 3 is repeated, except that the dried cobaltN-lauroylsarcosinate obtained (205 g) is dissolved in a mixture of 100 gof N-lauroylsarcosine and 700 ml of MTBE and is carbonylated withsynthesis gas (CO:H₂ ratio=2:1) at 120 bar in a steel autoclave. Thereaction is carried out at from 70 to 90° C.

The cobalt carbonyl formed can be used without limitation for theamidocarbonylation.

What is claimed is:
 1. A process for recovering cobalt carbonylcatalysts used in the preparation of N-acyl-alpha-amino acid derivativesby amidocarbonylation comprising the process steps:a--amidocarbonylatingN-acyl-alpha-amino acid derivatives in a solution forming a reactionsolution, b--adding aqueous hydrogen peroxide solution to the reactionsolution present after the preparation of the N-acyl-alpha-amino acidderivative forming an aqueous phase and non-aqueous product-containingphase, c--then separating the aqueous phase containing water-solublecobalt(II) salt from the non-aqueous product-containing phase,d--subsequently adding an alkali metal salt of the N-acyl-alpha-aminoacid derivative to the aqueous phase from the step c and forming aprecipitated cobalt salt, e--then separating off the precipitated cobaltsalt of the N-acyl-alpha-amino acid derivative to form a resultingcobalt salt, and f--finally converting the resulting cobalt salt of theN-acyl-alpha-amino acid derivative into the cobalt carbonyl catalyst inthe presence of a mixture of carbon monoxide and hydrogen.
 2. Theprocess as claimed in claim 1, wherein a mineral acid is, in addition tothe hydrogen peroxide, added to the reaction solution.
 3. The process asclaimed in claim 2, wherein the mineral acid is selected from the groupconsisting of hydrochloric acids, sulfuric acid and phosphoric acid. 4.The process as claimed in claim 2, wherein hydrogen peroxide is used inan amount of from 0.1 to 5 equivalents, based on the cobalt present inthe reaction solution.
 5. The process as claimed in claim 1, wherein,after the aqueous phase containing the water-soluble colbalt(II) salt isseparated off, the hydrogen peroxide present in this phase is removed.6. The process as claimed in claim 5, wherein the removal of thehydrogen peroxide is carried out by heating the aqueous phase.
 7. Theprocess as claimed in claim 5, wherein the aqueous phase is neutralizedwith alkali metal hydroxide before removal of the hydrogen peroxide. 8.The process as claimed in claim 1, wherein the alkali metal salt of theN-acyl-alpha-amino acid derivative is selected from the group consistingof the corresponding sodium and potassium salts.
 9. The process asclaimed in claim 1, wherein the alkali metal salt of theN-acyl-alpha-amino acid derivative is the corresponding alkali metalN-acylsarcosinate.
 10. The process as claimed in claim 1, wherein theprecipitated cobalt salt of the N-acyl-alpha-amino acid derivative iswashed and dried after the step d.
 11. The process as claimed in claim1, wherein the cobalt salt of the N-acyl-alpha-amino acid is reacted inthe form of a melt with the N-acyl-alpha-amino acid derivative for whosepreparation the cobalt carbonyl catalyst is intended.
 12. The process asclaimed in claim 1, wherein the converting in the presence of themixture of carbon monoxide and hydrogen is carried out at a temperatureof from 50 to 250° C.
 13. The process as claimed in claim 12, whereinthe converting in the presence of the mixture of carbon monoxide andhydrogen is carried out at a pressure of from 20 to 250 bar.
 14. Theprocess as claimed in claim 1, wherein the converting in the presence ofthe mixture of carbon monoxide and hydrogen is carried out at a pressureof from 20 to 250 bar.
 15. The process as claimed in claim 1, whereinthe concentration of water-soluble cobalt(II) salt present in theaqueous phase does not exceed 2% by weight.
 16. The process as claimedin claim 1, wherein the conversion of the resulting cobalt salt iscarried out in a polar, aprotic solvent.